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Discussion Starter #1
I have a tachometer i want to hook up to my 2003 Rebel250.
My problem is that the directions ask for "sparks per rotation"
Since the motor is twin cylinder and makes a wasted spark..what mode should i mode set the tach? 1 spark per revolution or 2 spark per revolution?
Im measuring RPM.
The wire to the tach wraps around one of the spark plug wires.
 

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I would think two sparks per revolution since if there wasn't a wasted spark, there would only be half the sparks. But what do I know?
 

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That's what I would think too.


Well if it revs up to 17,000 rpm, I think it'll be obvious it's on the wrong setting, :lol2:.
 

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The Rebel fires the spark plug on every revolution, even though it's a 4 stroke engine.
 

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Discussion Starter #5
Im only concerned with the left cylinder. ..i have a tach to measure rpm...my question is how many times does the spark plug fire on the left cylinder per rotation.
Thanks.
 

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Once per rotation, twice for all four strokes. It fires on compression and exhaust.
 

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As Guba first posted, each piston sparks once per rotation of the crankshaft, which is similar to a two stroke engine, even though it's a four stroke engine. If the tach reads one spark plug, I assume you would set it to two sparks since most engines fire each cylinder once per four stroke cycle (two rotations of crankshaft per cycle), and the Rebel does twice that.

Hope that doesn't confuse you.
 

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The tach is only reading sparks from one cylinder.
So does one cylinder fire once per rotation.....or does one one cylinder fire fire twice per rotation?
 

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while one cylinder is at top dead center of compression stroke the other cylinder is at TDC of exhaust stroke.. At this point Both cylinders fire at the same time.. Wasted Spark Ignition
both cylinders fire one time per rotation..
 

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while one cylinder is at top dead center of compression stroke the other cylinder is at TDC of exhaust stroke.. At this point Both cylinders fire at the same time.. Wasted Spark Ignition
both cylinders fire one time per rotation..
How does one measure RPM while only using one of the cylinders of a 2003 Honda Rebel CMX250C?
How many sparks per rotation of just one of the cylinders.
 

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The recommended idle speed, 1,400 rpm plus or minus 100, isn't set just to provide smooth engine performance, it also ensures adequate oil circulation. So going below the recommended idle speed could damage the engine due to oil starvation. Those engineers may have learned by trial and error, which I doubt, but we disregard their guidance at the risk of damaging something.
 

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As stated before, travelling at 20 mph in fifth gear lugs the engine, which isn't good for it. This explains why:

Minimum cruising speed in fifth gear, per the Rebel owner's manual, is 30 mph. And should you need to accelerate quickly at that speed while in fifth, a downshift is recommended to avoid lugging the engine. Lugging the engine isn't going to improve fuel economy; it will be worse.
 

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Well, I don't know what else to say, flite. My experience is "improved" ride quality and engine stability with a wider range of deeper carburetor throttle...….. How about if I get over 88mpg, then will you believe me? :^)
There are limits to what the engine is capable of. Getting 88 mpg doing 20 mph in fifth at full throttle isn't possible, even assuming the engine wouldn't die trying.

We had a member here a few years back that claimed increased top speed (like well over 90 mph) and mileage (over 100 mpg) with extremely high gearing. I don't think anyone here believed him.
 

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There are limits to what the engine is capable of. Getting 88 mpg doing 20 mph in fifth at full throttle isn't possible, even assuming the engine wouldn't die trying.

We had a member here a few years back that claimed increased top speed (like well over 90 mph) and mileage (over 100 mpg) with extremely high gearing. I don't think anyone here believed him.
I think that member was doing all his testing on a long steep downhill. Many have tried, none have succeeded in installing higher ratio sprockets AND maintaining top end speed.
 

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He was in Miami, FL. There were no hills anywhere near him.
 
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